1. Field of the Invention
This invention relates to a dental radiographic apparatus, and more particularly to a dental radiographic apparatus for an entire jaw having a rotary arm comprising means for detecting the shape of the object and means for controlling the rotation speed of the arm and the feeding speed of X-ray film.
2. Prior Art
Medical examination made by use of tomography of a curved plane has been playing a very important role in dental treatment in recent years, and the fact that an X-ray photographic image obtained by this photography is clear and sharp and free from distortions makes it indispensable for exact treatment free from a mistaken diagnosis.
But the conventional radiographic apparatuses for photographing the entire jaws, of the type described above, are usually nothing but proposals for a photographic apparatus which can embody the theoretically elucidated tomography of a curved plane into a practical form. For example, mostly apparatuses constructed so as to obtain a desired panoramic X-ray photograph by controlling the amount of X-rays irradiated upon an object by synchronously changing the rotatingly moving speed of an X-ray generator and the feed speed of an X-ray film by arrangement of mechanically connected parts in the apparatus, so to speak, apparatuses designed to make synchronous control fo the moving speed of the X-ray generator and the feed speed of X-ray film and intended primarily to elucidate tomography of a curved plane in relation with the principle of the tomography.
In the apparatuses of the type described above, despite the fact that they have rendered it possible to make practical use of a panormaic X-ray photograph of the entire jaws by tomography of a curved plane, limited characteristic traits of the mechanical structure thereof have made it difficult to prevent distortions and provide uniform density in the resulting picture. Accordingly, when a tomographic picture of a curved plane was taken by controlling the feed speed of film in synchronism with the rotation speed of the rotary arm, it was difficult or next to impossible to prevent distortions of the image and lack of unformity in density in the picture obtained, and especially in the X-ray photographic image of the front tooth region, it was impossible to prevent not only lack of sharpness of the image caused by shortage of density in the X-ray photographic image due to the presence of the cervical vertebrae but also to nonuniformity in a rate of enlargement of the individual tooth images in the dental arch.